Naji Al-Khudairi1, Shigeru Kobayashi2, Adam Meir1. 1. Victor Horsley Department of Neurosurgery, The National Hospital for Neurology and Neurosurgery, University College London, Queen Square, London WC1N 3BG, England. 2. Department of Spine Surgery, University of Fukui, 23-3 Matsuokashimoaizuki, Eiheiji-cho, Yoshida-gun, Fukui Prefecture, Japan.